Avian limb morphogenesis has been shown to involve a complex set of tissue interactions between the mesoderm and ectoderm. This proposed research will investigate the nature and possible mechanisms of such interactions. This work includes three principal areas of research: (1) the nature of interactions between mesoderm and ectoderm of limbs whose morphogenesis is altered by mutation, (2) interactions in genetically normal limbs, and (3) tissue interactions in the mammalian limb. In vitro methods for analyzing morphogenetic activities are being developed. In addition mesoderm-ectoderm interchanges and histological analysis will aid in our analysis of limb morphogenesis.